Dual and multi-position valves to inject, select or switch fluids are well established in scientific instrumentation. In particular, high pressure multiport or multi-position valves are applied in analytical processes, such as liquid chromatography. High pressure applications for micro-fluidic distribution management benefits from faster separations and increased through put. In order to accurately run these applications, positioning of the valve must be very precise. The more precise the positioning is, the lower the effects of dispersion will have on the analysis.
These high pressure micro-fluidic distribution management systems typically include a drive motor, the multi-position valve with a valve actuator assembly mounted between the drive motor and the multi-position valve. More recently, these multi-position valves assemblies incorporate internal encoder devices within a housing of the actuator assembly that are applied to determine the position of the multi-position valve.
The encoder device generally includes an encoder wheel coupled to a rotating shaft of the valve, and rotates around the shaft axis. The encoder device also includes an encoder module mounted to the actuator housing that cooperates with the encoder wheel to determine the rotational position of wheel relative to the shaft axis.
To properly operate these encoder devices, the positioning and the alignment between the encoder module and the encoder wheel is critical. For example, in some current designs, the angular relation of the encoder wheel and the shaft must be set during assembly, as any variation will cause variation in the valve's angular position. In other designs, it is imperative that the concentricity throughout the drive train of the valve is maintained within very tight tolerances. That is, all of the mating parts must be substantially aligned or the valve may bind up. This is especially important when installing the encoder wheel on the rotating shaft, and the encoder module to the actuator housing, as there is very little run out allowed for the parts to operate properly. If the encoder module is installed independently of the encoder wheel, it is very important that the shaft of the encoder wheel is mounted to be very tightly toleranced with respect to run-out and concentricity. Due to these tight tolerances, the cost of the actuator is higher and more difficult to assemble.
In still other designs, the encoder wheel is secured to the shaft with a set screw. Thus, it is possible in these designs that the set screw will “back off” and allow the encoder wheel to move relative to the shaft. This would cause the encoding to be incorrect and the valve would not position correctly.
Accordingly, there is a need for a multi-position micro-fluidic valve actuator system that simplifies installation of the encoder assembly during actuator assembly.